Thousands of freshers who should have been given a life-saving jab ahead of them starting university are at an increased risk of meningitis, the Department of Health has warned.

Any first-time university student under the age of 25 who has not yet received the meningococcal C vaccine has been urged to contact their GP as soon as possible.

Around 23,000 A-Level students from Northern Ireland have been advised to receive the injection, which protects against the potentially fatal meningococcus bacteria that can cause meningitis and septicaemia.

The Department of Health launched the mass inoculation programme over the summer holidays and it is expected to run for four years at a cost of around £700,000.

It has been specifically targeted at anyone under 25, who will be starting university this autumn as they have been highlighted to be most at risk from the disease after a change in vaccination schedules last year.

It was found that the dose administered to babies at 16 weeks does not provide adequate protection against meningococcal C. That jab has now been removed in favour of an adolescent booster, administered by the school health service in Year 11.

The Joint Committee on Vaccination and Immunisation (JCVI) recommended the catch-up programme for university freshers. However, those under 25 will not have received the newly introduced booster in Year 11 and "therefore they may be at higher risk of contracting meningococcal C", chief medical officer Dr Michael McBride has advised in a letter.

He added that the "increased risk is particularly associated with attending university" and "the increased risk is to first-year students, particularly in the first few weeks of university".

Students have been advised of the catch-up scheme through their schools and Ucas.

Although Dr McBride has recommended young people should receive the Men C vaccine at least two weeks before they are due to start university to "ensure a full immune response", it is not too late to be vaccinated.

This year's programme is due to run until October and next year's will run between June and October, with students being advised to contact their GP as soon as they finish their exams in 2015.